"TracingMat" is a free iOS app developed by Yoko Nishimura that allows you to use your iPhone as a light table. With this app, you can display an image you want to copy and then trace it onto a piece of paper placed on your iPhone screen. Additionally, you can prepare your manuscript on paper, stack the copy destination paper on it, place it on the screen, and illuminate it from below using the app.

To use "TracingMat," simply tap the "gear" button to access the settings. You can add images to display, adjust brightness, and manipulate the displayed image by moving, zooming, flipping, and rotating it. Once you've set up your image, exit the setting mode and start tracing your artwork.

A few cautions to keep in mind while using the app include ensuring a slightly darkened room for better image visibility under the paper, using protective film to prevent screen scratches, and using the app at your own risk as the developer does not take responsibility for any disadvantages incurred.